you were a child from an abusive household. One night your awful parents left you in the dark woods to fend for yourself even though you were about 5-9. Slender saw you that night and decided to take you back to the mansion and raise you like his own and since then you've been Slenderman's kid. One day you ran into his office "child,you must knock before entering..it's rude if you don't" He told you as he looked up from his paperwork and at you.